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data-v-06225672><a href="https://github.com/linxin1123" target="_blank" title="作者" class="beLink" data-v-06225672>lingxin</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>2023-02-26</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="">JavaScript(四)<!----></h1>  <div class="theme-vdoing-content content__default"><h1 id="javascript-四"><a href="#javascript-四" class="header-anchor">#</a> JavaScript(四)</h1> <h2 id="题目目录"><a href="#题目目录" class="header-anchor">#</a> 题目目录</h2> <ol><li><a href="#q1">gulp是什么</a></li> <li><a href="#q2">说一下Vue的双向数据绑定</a></li> <li><a href="#q3">事件的各个阶段</a></li> <li><a href="#q4">let var const</a></li> <li><a href="#q5">快速的让一个数组乱序</a></li> <li><a href="#q6">如何渲染几万条数据并不卡住页面</a></li> <li><a href="#q7">希望获取到页面中所有的checkbox怎么做</a></li> <li><a href="#q8">怎样添加、移除、移动、复制、创建、查找节点</a></li> <li><a href="#q9">正则表达式</a></li> <li><a href="#q10">JavaScript中callee和caller的作用</a></li> <li><a href="#q11">window.onload和$(document).ready</a></li> <li><a href="#q12">addEventListener()和attachEvent的区别</a></li> <li><a href="#q13">获取页面所有的checkbox</a></li> <li><a href="#q14">数组去重方法总结</a></li> <li><a href="#q15">(设计题)想实现一个对页面某个节点的拖拽？如何做？（使用原生JS）</a></li> <li><a href="#q16">JavaScript全局函数和全局变量</a></li> <li><a href="#q17">使用js实现一个持续的动画效果</a></li> <li><a href="#q18">封装一个函数，参数是定时器的时间，.then执行回调函数</a></li> <li><a href="#q19">怎么判断两个对象相等</a></li> <li><a href="#q20">项目做过哪些性能优化</a></li></ol> <h3 id="q1">1. gulp是什么</h3> <ul><li>gulp是前端开发过程中一种基于流的代码构建工具，是自动化项目的构建利器，它不仅能对网站资源进行优化，而且在开发过程中很多重复的任务能够使用正确的工具自动完成</li> <li>Gulp的核心概念：流</li> <li>流：简单来说就是建立在面向对象基础上的一种抽象的数据处理工具，在流中，定义了一些处理数据的基本操作，如读取数据，写入数据等，程序员对流进行所有操作的，而不用关心流的另一头数据的真正流向</li> <li>gulp正是通过流和代码优于配置的策略来尽量简化任务编写的工作</li> <li>Gulp的特点
<ul><li>易于使用：通过代码由于配置的策略，gulp让任务简单，复杂的任务可管理</li> <li>构建快速，利用node.js流的威力，你可以快速构建项目并减少频繁的IO操作</li> <li>易于学习：最少的api，掌握gulp毫不费力，构建工作尽在掌握，如同一些列流管道</li></ul></li></ul> <h3 id="q2">2. 说一下Vue双向数据绑定的原理</h3> <ul><li>vue.js则是采用数据劫持结合发布者-订阅者模式的方式，通过Object.defineProperty()来劫持各个属性的setter，getter，在数据变动时发布消息给订阅者，触发相应的监听回调</li></ul> <h3 id="q3">3. 事件的各个阶段</h3> <ul><li>捕获阶段----&gt;目标阶段-----&gt;冒泡阶段</li> <li>document---&gt;target目标-----&gt;document</li> <li>由此，addEventListener的第三个参数
<ul><li>true表示捕获阶段响应时间</li> <li>false表示冒泡阶段响应时间</li></ul></li></ul> <h3 id="q4">4. let var const </h3> <ul><li>let
<ul><li>作用域被限制在块级中的变量</li> <li>无变量提升</li> <li>从块开始到初始化处理存在暂时性死区</li></ul></li> <li>var
<ul><li>函数作用域</li> <li>变量提示</li> <li>重复声明</li></ul></li> <li>const
<ul><li>只读引用</li> <li>定义时需要初始化</li></ul></li></ul> <h3 id="q5">5. 快速的让一个数组乱序 </h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> arr<span class="token operator">=</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">,</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">,</span><span class="token number">7</span><span class="token punctuation">,</span><span class="token number">8</span><span class="token punctuation">,</span><span class="token number">9</span><span class="token punctuation">,</span><span class="token number">10</span><span class="token punctuation">]</span>
arr<span class="token punctuation">.</span><span class="token function">sort</span><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">return</span> Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">-</span><span class="token number">0.5</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>

console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>arr<span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><h3 id="q6">6. 如何渲染几万条数据并不卡住页面 </h3> <ul><li>一次渲染部分DOM，使用requestAnimationFrame来每16ms刷新一次</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token operator">&lt;</span><span class="token operator">!</span><span class="token constant">DOCTYPE</span> html<span class="token operator">&gt;</span>
<span class="token operator">&lt;</span>html lang<span class="token operator">=</span><span class="token string">&quot;en&quot;</span><span class="token operator">&gt;</span>

<span class="token operator">&lt;</span>head<span class="token operator">&gt;</span>
    <span class="token operator">&lt;</span>meta charset<span class="token operator">=</span><span class="token string">&quot;UTF-8&quot;</span><span class="token operator">&gt;</span>
    <span class="token operator">&lt;</span>meta http<span class="token operator">-</span>equiv<span class="token operator">=</span><span class="token string">&quot;X-UA-Compatible&quot;</span> content<span class="token operator">=</span><span class="token string">&quot;IE=edge&quot;</span><span class="token operator">&gt;</span>
    <span class="token operator">&lt;</span>meta name<span class="token operator">=</span><span class="token string">&quot;viewport&quot;</span> content<span class="token operator">=</span><span class="token string">&quot;width=device-width, initial-scale=1.0&quot;</span><span class="token operator">&gt;</span>
    <span class="token operator">&lt;</span>title<span class="token operator">&gt;</span>Document<span class="token operator">&lt;</span><span class="token operator">/</span>title<span class="token operator">&gt;</span>
<span class="token operator">&lt;</span><span class="token operator">/</span>head<span class="token operator">&gt;</span>

<span class="token operator">&lt;</span>body<span class="token operator">&gt;</span>
    <span class="token operator">&lt;</span>ul<span class="token operator">&gt;</span>控件<span class="token operator">&lt;</span><span class="token operator">/</span>ul<span class="token operator">&gt;</span>
    <span class="token operator">&lt;</span>script<span class="token operator">&gt;</span>

        <span class="token function">setTimeout</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
            <span class="token comment">// 十万条数据</span>
            <span class="token keyword">const</span> total <span class="token operator">=</span> <span class="token number">100000</span>

            <span class="token comment">// 每次渲染20条，</span>
            <span class="token keyword">const</span> once <span class="token operator">=</span> <span class="token number">20</span>

            <span class="token comment">// 渲染次数</span>
            <span class="token keyword">const</span> renderCount <span class="token operator">=</span> total <span class="token operator">/</span> once

            <span class="token comment">// 当前渲染次数</span>
            <span class="token keyword">let</span> currCount <span class="token operator">=</span> <span class="token number">0</span>


            <span class="token keyword">let</span> ul <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">querySelector</span><span class="token punctuation">(</span><span class="token string">&quot;ul&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

            <span class="token keyword">function</span> <span class="token function">add</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
                <span class="token comment">// 优化性能，插⼊不会造成回流</span>
                <span class="token keyword">const</span> fragment <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">createDocumentFragment</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> once<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
                    <span class="token keyword">const</span> li <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span><span class="token string">&quot;li&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                    li<span class="token punctuation">.</span>innerText <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">*</span> total<span class="token punctuation">)</span><span class="token punctuation">;</span>
                    fragment<span class="token punctuation">.</span><span class="token function">appendChild</span><span class="token punctuation">(</span>li<span class="token punctuation">)</span><span class="token punctuation">;</span>
                <span class="token punctuation">}</span>
                ul<span class="token punctuation">.</span><span class="token function">appendChild</span><span class="token punctuation">(</span>fragment<span class="token punctuation">)</span><span class="token punctuation">;</span>
                currCount <span class="token operator">+=</span> <span class="token number">1</span><span class="token punctuation">;</span>
                <span class="token function">loop</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token punctuation">}</span>
            <span class="token keyword">function</span> <span class="token function">loop</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
                <span class="token keyword">if</span> <span class="token punctuation">(</span>currCount <span class="token operator">&lt;</span> renderCount<span class="token punctuation">)</span> <span class="token punctuation">{</span>
                    window<span class="token punctuation">.</span><span class="token function">requestAnimationFrame</span><span class="token punctuation">(</span>add<span class="token punctuation">)</span><span class="token punctuation">;</span>
                <span class="token punctuation">}</span>
            <span class="token punctuation">}</span>
            <span class="token function">loop</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>


        <span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span>


    <span class="token operator">&lt;</span><span class="token operator">/</span>script<span class="token operator">&gt;</span>
<span class="token operator">&lt;</span><span class="token operator">/</span>body<span class="token operator">&gt;</span>

<span class="token operator">&lt;</span><span class="token operator">/</span>html<span class="token operator">&gt;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br><span class="line-number">57</span><br></div></div><h3 id="q7">7. 希望获取到页面中所有的checkbox怎么做 </h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> domList<span class="token operator">=</span>document<span class="token punctuation">.</span><span class="token function">getElementsByTagName</span><span class="token punctuation">(</span><span class="token string">&quot;input&quot;</span><span class="token punctuation">)</span>

domList<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span><span class="token parameter">item</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
    <span class="token keyword">return</span> item<span class="token punctuation">.</span>type<span class="token operator">===</span><span class="token string">'checkbox'</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><h3 id="q8">8. 怎样添加、移除、移动、复制、创建、查找节点 </h3> <ul><li>创建新节点</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token function">createDocumentFragment</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 创建DOM片段</span>
<span class="token function">craeteElement</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 创建具体的元素</span>
<span class="token function">createTextNode</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 创建一个文本节点</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><ul><li>添加，移除，替换、插入</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token function">appendChild</span><span class="token punctuation">(</span><span class="token punctuation">)</span>  <span class="token comment">// 添加</span>
<span class="token function">removeChild</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 移除</span>
<span class="token function">replaceChild</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 替换</span>
<span class="token function">insertBefore</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 插入</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><ul><li>查找</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token function">getElementsByTagName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 根据标签名</span>
<span class="token function">getElementsByName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 元素name属性</span>
<span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token punctuation">)</span>  <span class="token comment">// 元素id</span>

<span class="token function">querySelector</span><span class="token punctuation">(</span>选择器<span class="token punctuation">)</span>
<span class="token function">querySelectorAll</span><span class="token punctuation">(</span>选择器<span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><h3 id="q9">9. 正则表达式 </h3> <ul><li>正则表达式构造函数var reg=new RegExp(&quot;xxx&quot;)与正则表达式字面量var reg=// 有什么不同</li> <li>使用RegExp()构造函数的时候，不仅需要转义引号(<code>\</code>表示)，并且还需要双反斜杆（即<code>\\</code>表示一个<code>\</code>），使用正则表达式字面量的效率更高</li></ul> <h3 id="q10">10. JavaScript中callee和caller的作用 </h3> <ul><li>caller是返回一个对函数的引用</li> <li>callee是返回正在被执行的function函数，也就是所指定的function对象的正文</li></ul> <blockquote><p>那么问题来了？如果⼀对兔⼦每⽉⽣⼀对兔⼦；⼀对新⽣兔，从第⼆个⽉起就
开始⽣兔⼦；假定每对兔⼦都是⼀雌⼀雄，试问⼀对兔⼦，第n个⽉能繁殖成
多少对兔⼦？（使⽤ callee 完成）</p></blockquote> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> result<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>

<span class="token keyword">function</span> <span class="token function">fn</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    
    <span class="token keyword">if</span><span class="token punctuation">(</span>n<span class="token operator">===</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token number">1</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span><span class="token keyword">else</span> <span class="token keyword">if</span><span class="token punctuation">(</span>n<span class="token operator">===</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token number">1</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
        <span class="token keyword">if</span><span class="token punctuation">(</span>result<span class="token punctuation">[</span>n<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            <span class="token keyword">return</span> result<span class="token punctuation">[</span>n<span class="token punctuation">]</span>
        <span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
            result<span class="token punctuation">[</span>n<span class="token punctuation">]</span><span class="token operator">=</span>arguments<span class="token punctuation">.</span><span class="token function">callee</span><span class="token punctuation">(</span>n<span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token operator">+</span>arguments<span class="token punctuation">.</span><span class="token function">callee</span><span class="token punctuation">(</span>n<span class="token operator">-</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            
            <span class="token keyword">return</span> result<span class="token punctuation">[</span>n<span class="token punctuation">]</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div><h3 id="q11">11. window.onload和$(document).ready </h3> <blockquote><p>原⽣ JS 的 window.onload 与 Jquery 的 $(document).ready(function()
{}) 有什么不同？如何⽤原⽣JS实现Jq的 ready ⽅法？</p></blockquote> <ul><li>window.onload()方法是必须等到页面内包括图片的所有元素加载完毕后才能执行</li> <li>$(document).ready()是DOM结构绘制完毕后就执行，不比等到加载完成</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">ready</span><span class="token punctuation">(</span><span class="token parameter">fn</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    
    <span class="token keyword">if</span><span class="token punctuation">(</span>document<span class="token punctuation">.</span>addEventListener<span class="token punctuation">)</span><span class="token punctuation">{</span>
        document<span class="token punctuation">.</span><span class="token function">addEventListener</span><span class="token punctuation">(</span><span class="token string">'DOMContentLoaded'</span><span class="token punctuation">,</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            document<span class="token punctuation">.</span><span class="token function">removeEventListener</span><span class="token punctuation">(</span><span class="token string">'DOMContentLoaded'</span><span class="token punctuation">,</span><span class="token function">arguments</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>fn<span class="token punctuation">)</span><span class="token punctuation">)</span>
            <span class="token function">fn</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span><span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">)</span>
        
        
    <span class="token punctuation">}</span><span class="token keyword">else</span> <span class="token keyword">if</span><span class="token punctuation">(</span>document<span class="token punctuation">.</span>attachEvent<span class="token punctuation">)</span><span class="token punctuation">{</span>
        
        <span class="token comment">// IE</span>
        document<span class="token punctuation">.</span><span class="token function">attachEvent</span><span class="token punctuation">(</span><span class="token string">'onreadystateChange'</span><span class="token punctuation">,</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            
            <span class="token keyword">if</span><span class="token punctuation">(</span>document<span class="token punctuation">.</span>readyState<span class="token operator">===</span><span class="token string">'complete'</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
                document<span class="token punctuation">.</span><span class="token function">detachEvent</span><span class="token punctuation">(</span><span class="token string">'onreadystateChange'</span><span class="token punctuation">,</span>arguments<span class="token punctuation">.</span><span class="token function">caller</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                <span class="token function">fn</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span><span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">)</span>
        
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br></div></div><h3 id="q12">12. addEventListener()和attachEvent的区别 </h3> <ul><li>addEventListener()是符合W3C规范的标准方法，attachEvent()是IE低版本的非标准写法</li> <li>addEventListener() ⽀持事件冒泡和事件捕获; - ⽽ attachEvent() 只⽀持事件冒泡</li> <li>addEventListener()第一个参数不需要加'on',attachEvent()需要加on</li> <li>如果为同⼀个元素绑定多个事件, addEventListener() 会按照事件绑定的顺序依次执⾏,
attachEvent() 会按照事件绑定的顺序倒序执⾏</li></ul> <h3 id="q13">13. 获取页面所有的checkbox </h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> resultArr<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>

<span class="token keyword">var</span> input<span class="token operator">=</span>document<span class="token punctuation">.</span><span class="token function">quselectorAll</span><span class="token punctuation">(</span><span class="token string">'input'</span><span class="token punctuation">)</span>

<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">var</span> i<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>i<span class="token operator">&lt;</span>input<span class="token punctuation">.</span>length<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>input<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">.</span>type<span class="token operator">===</span><span class="token string">'checkbox'</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        resultArr<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>input<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><h3 id="q14">14.数组去重方法总结 </h3> <ul><li>es6 Set去重</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">unique</span><span class="token punctuation">(</span><span class="token parameter">arr</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">return</span> Array<span class="token punctuation">.</span><span class="token function">from</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Set</span><span class="token punctuation">(</span>arr<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><ul><li>es5 for循环</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">var</span> i<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>i<span class="token operator">&lt;</span>arr<span class="token punctuation">.</span>length<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">var</span> j<span class="token operator">=</span>i<span class="token operator">+</span><span class="token number">1</span><span class="token punctuation">;</span>j<span class="token operator">&lt;</span>arr<span class="token punctuation">.</span>length<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">if</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">===</span>arr<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            arr<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span>j<span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">)</span>
            j<span class="token operator">--</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><ul><li>indexOf去重，新数组里面没有的塞入，有的不管</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> i<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>i<span class="token operator">&lt;</span>arr<span class="token punctuation">.</span>length<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>newArr<span class="token punctuation">.</span><span class="token function">indexOf</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token operator">===</span><span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        newArr<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><ul><li>sort,然后根据前一项和后一项的不同，后一项无限往后走，直到找到和前面不一样的</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code>arr<span class="token operator">=</span>arr<span class="token punctuation">.</span><span class="token function">sort</span><span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token keyword">var</span> newArr<span class="token operator">=</span><span class="token punctuation">[</span>arr<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">]</span>

<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> i<span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">;</span>i<span class="token operator">&lt;</span>arr<span class="token punctuation">.</span>length<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">!==</span>arr<span class="token punctuation">[</span>i<span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        newArr<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><ul><li>使用对象，键就是属性</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> newArr<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>
<span class="token keyword">var</span> obj<span class="token operator">=</span><span class="token punctuation">{</span><span class="token punctuation">}</span>

<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> i<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>i<span class="token operator">&lt;</span>arr<span class="token punctuation">.</span>length<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    
    <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span>obj<span class="token punctuation">[</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        arr<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token parameter">arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span></span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            obj<span class="token punctuation">[</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token operator">=</span><span class="token number">1</span>
        <span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
            obj<span class="token punctuation">[</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token operator">++</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><ul><li>利用includes</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> array <span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
 <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">var</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> arr<span class="token punctuation">.</span>length<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
 <span class="token keyword">if</span><span class="token punctuation">(</span> <span class="token operator">!</span>array<span class="token punctuation">.</span><span class="token function">includes</span><span class="token punctuation">(</span> arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token comment">//includes 检测数组是否有某个值</span>
 array<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token punctuation">}</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><ul><li>利用hasOwnProperty</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> obj<span class="token operator">=</span><span class="token punctuation">{</span><span class="token punctuation">}</span>

<span class="token keyword">return</span> arr<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span><span class="token punctuation">(</span>item<span class="token punctuation">,</span>index<span class="token punctuation">,</span>arr<span class="token punctuation">)</span><span class="token punctuation">{</span>
                  
                  <span class="token keyword">return</span> obj<span class="token punctuation">.</span><span class="token function">hasOwnProperty</span><span class="token punctuation">(</span><span class="token keyword">typeof</span> item<span class="token operator">+</span>item<span class="token punctuation">)</span><span class="token operator">?</span> <span class="token boolean">false</span><span class="token operator">:</span><span class="token punctuation">(</span>obj<span class="token punctuation">[</span><span class="token keyword">typeof</span> item<span class="token operator">+</span>item<span class="token punctuation">]</span><span class="token punctuation">)</span>
                  <span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><ul><li>利用filter</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">return</span> arr<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">item<span class="token punctuation">,</span> index<span class="token punctuation">,</span> arr</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
 <span class="token comment">//当前元素，在原始数组中的第⼀个索引==当前索引值，否则返回当前元素</span>
 <span class="token keyword">return</span> arr<span class="token punctuation">.</span><span class="token function">indexOf</span><span class="token punctuation">(</span>item<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token operator">===</span> index<span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><ul><li>递归去重，从后往前，当前项不等于前面一项，往前，相等，则去掉当前项</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">loop</span><span class="token punctuation">(</span><span class="token parameter">index</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
 <span class="token keyword">if</span><span class="token punctuation">(</span>index <span class="token operator">&gt;=</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
 <span class="token keyword">if</span><span class="token punctuation">(</span>array<span class="token punctuation">[</span>index<span class="token punctuation">]</span> <span class="token operator">===</span> array<span class="token punctuation">[</span>index<span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
 array<span class="token punctuation">.</span><span class="token function">splice</span><span class="token punctuation">(</span>index<span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token function">loop</span><span class="token punctuation">(</span>index <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//递归loop，然后数组去重</span>
 <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token function">loop</span><span class="token punctuation">(</span>len<span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><ul><li>map去重</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> i<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>i<span class="token operator">&lt;</span>arr<span class="token punctuation">.</span>length<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">has</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        map<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">,</span><span class="token boolean">true</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
        map<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">)</span>
        newArr<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><h3 id="q15">15.(设计题)想实现一个对页面某个节点的拖拽？如何做？（使用原生JS） </h3> <ul><li>给需要拖拽的节点绑定mousedown，mousemove，mouseup事件</li> <li>mouseDown事件触发收，开始拖拽</li> <li>mouseMove是，通过event.clientX,event.clientY获取拖拽位置，实时更新</li> <li>mouseup是，拖拽结束</li></ul> <h3 id="q16">16.Javascript全局函数和全局变量 </h3> <ul><li>全局变量
<ul><li>Infinity 代表正的无穷大的数值</li> <li>NaN 指示某个值不是数字值</li> <li>undefined指示未定义的值</li></ul></li> <li>全局函数
<ul><li>decodeURI()解析某个编码的URI</li> <li>decodeURIComponent(),解码一个编码的URI组件</li> <li>encodeURI() 字符串编码为URI</li> <li>encodeURIComponent():把字符串编码为URI组件</li> <li>escape()对字符串进行编码</li> <li>eval()计算JavaScript字符串，并把它作为脚本代码来执行</li> <li>isFinite(),检查某个值是否为有穷大的数</li> <li>isNaN()检查某个值是否为数字</li> <li>Number()，把对象的值转换为数字</li> <li>parseFloat() 解析一个字符串并返回一个浮动数</li> <li>parseInt()解析一个字符串并返回一个整数</li> <li>String()把对象的值转换为字符串</li> <li>unescape() 对由escape()编码的字符串进行解码</li></ul></li></ul> <h3 id="q17">17.使用js实现一个持续的动画效果 </h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> e<span class="token operator">=</span>document<span class="token punctuation">.</span><span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token string">&quot;e&quot;</span><span class="token punctuation">)</span>

<span class="token keyword">var</span> flag<span class="token operator">=</span><span class="token boolean">true</span>

<span class="token keyword">var</span> left<span class="token operator">=</span><span class="token number">0</span>

<span class="token function">setInterval</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
    
    left<span class="token operator">==</span><span class="token number">0</span><span class="token operator">?</span> flag<span class="token operator">=</span><span class="token boolean">true</span><span class="token operator">:</span>left<span class="token operator">==</span><span class="token number">100</span><span class="token operator">?</span> flag<span class="token operator">=</span><span class="token boolean">false</span><span class="token operator">:</span><span class="token string">''</span>
    
    flag<span class="token operator">?</span> e<span class="token punctuation">.</span>style<span class="token punctuation">.</span>left<span class="token operator">=</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>left<span class="token operator">++</span><span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">px</span><span class="token template-punctuation string">`</span></span><span class="token operator">:</span>e<span class="token punctuation">.</span>style<span class="token punctuation">.</span>left<span class="token operator">=</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>left<span class="token operator">--</span><span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">px</span><span class="token template-punctuation string">`</span></span>
<span class="token punctuation">}</span><span class="token punctuation">,</span><span class="token number">1000</span><span class="token operator">/</span><span class="token number">60</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><ul><li>兼容性处理</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token comment">//兼容性处理</span>
window<span class="token punctuation">.</span>requestAnimFrame <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
 <span class="token keyword">return</span> window<span class="token punctuation">.</span>requestAnimationFrame <span class="token operator">||</span>
 window<span class="token punctuation">.</span>webkitRequestAnimationFrame <span class="token operator">||</span>
 window<span class="token punctuation">.</span>mozRequestAnimationFrame <span class="token operator">||</span>
 <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">callback</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
 window<span class="token punctuation">.</span><span class="token function">setTimeout</span><span class="token punctuation">(</span>callback<span class="token punctuation">,</span> <span class="token number">1000</span> <span class="token operator">/</span> <span class="token number">60</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">var</span> e <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token string">&quot;e&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">var</span> flag <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
<span class="token keyword">var</span> left <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword">function</span> <span class="token function">render</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
 left <span class="token operator">==</span> <span class="token number">0</span> <span class="token operator">?</span> flag <span class="token operator">=</span> <span class="token boolean">true</span> <span class="token operator">:</span> left <span class="token operator">==</span> <span class="token number">100</span> <span class="token operator">?</span> flag <span class="token operator">=</span> <span class="token boolean">false</span> <span class="token operator">:</span> <span class="token string">''</span><span class="token punctuation">;</span>
 flag <span class="token operator">?</span> e<span class="token punctuation">.</span>style<span class="token punctuation">.</span>left <span class="token operator">=</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string"> </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>left<span class="token operator">++</span><span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">px</span><span class="token template-punctuation string">`</span></span> <span class="token operator">:</span>
 e<span class="token punctuation">.</span>style<span class="token punctuation">.</span>left <span class="token operator">=</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string"> </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>left<span class="token operator">--</span><span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">px</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">(</span><span class="token keyword">function</span> <span class="token function">animloop</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
 <span class="token function">render</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token function">requestAnimFrame</span><span class="token punctuation">(</span>animloop<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br></div></div><h3 id="q18">18.封装一个函数，参数是定时器的时间，.then执行回调函数 </h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">sleep</span><span class="token punctuation">(</span><span class="token parameter">time</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">Promise</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">resolve</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token function">setTimeout</span><span class="token punctuation">(</span>reslove<span class="token punctuation">,</span>time<span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><h3 id="q19">19.怎么判断两个对象相等 </h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token constant">JSON</span><span class="token punctuation">.</span><span class="token function">stringify</span><span class="token punctuation">(</span>obj<span class="token punctuation">)</span><span class="token operator">==</span><span class="token constant">JSON</span><span class="token punctuation">.</span><span class="token function">stringify</span><span class="token punctuation">(</span>obj2<span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h3 id="q20">20.项目做过哪些性能优化 </h3> <ul><li><p>减少HTTP请求</p></li> <li><p>减少DNS查询</p></li> <li><p>使用CDN</p></li> <li><p>避免重定向</p></li> <li><p>图片懒加载</p></li> <li><p>减少DOM操作</p></li> <li><p>使用外部JavaScript</p></li> <li><p>使用iconfont</p></li> <li><p>使用css 精灵图</p></li></ul></div></div>  <div class="page-edit"><div class="edit-link"><a href="https://github.com/linxin1123/vuepress-blog/edit/master/docs/08.面试/02.前端面试/01.基础篇/08.JavaScript(四).md" target="_blank" rel="noopener noreferrer">编辑</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <!----> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2023/02/26, 19:02:51</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/pages/552413/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">JavaScript(三)</div></a> <a href="/pages/97a8a1/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">JavaScript(五)</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
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